open docs / kern audio

what open does

open is an algorithmic reverb that listens to the source spectrum and changes decay times by frequency. i use focus to set how much the source affects the tail, then bloom to choose whether stronger bands decay sooner or later.

what open is not for

i would not choose open to reproduce a particular sampled room or hardware plate.
i would not use it to remove room sound already recorded into a source.
i would not expect reverse to create a swell before an incoming live note.
i would not expect length to guarantee one identical decay time across every frequency and character.

controls

these are parameter defaults. loading a preset can change them. the tail eq has four editable bands.

control	range	default	what it does
depth	0 to 100%	30%	blends dry input with reverb using an equal-power curve. at 100%, the dry contribution is removed.
length	0.1 to 12 s	1.8 s	sets the decay-time reference. actual decay varies by frequency and character. at 11.95 s and above, it enters freeze.
focus	0 to 100%	40%	sets how strongly the source spectrum changes decay times. bloom determines whether stronger bands decay sooner or later.
bloom	0 to 100%	60%	shortens stronger bands below 50% and extends them above 50%. at 50%, focus has no effect on the decay-time mapping.
tone	-6 to +6 db	0 db	applies opposing low and high shelves to the reverb. the dry signal is unchanged.
character	room / hall / cloud	hall	selects delay, diffusion and decay settings. room and hall add early reflections. cloud omits those reflections and spreads incoming excitation over one second.
m/s	off / on	off	encodes the wet processing input as mid and side, then decodes it before mixing with dry. source analysis uses the mid signal.
delta	off / on	off	isolates the wet signal at the current depth, with auto comp bypassed. it does not subtract the dry waveform from the reverb.
auto comp	off / on	on	adjusts wet gain against dry loudness, holding gain during freeze and reverse. delta bypasses it. cloud applies no compensation even when the button is on.
sidechain enable	off / on	off	enables ducking from an external sidechain when connected, otherwise from the dry input. the key reduces level; spectral analysis keeps listening to the main input.
sidechain target	wet / all	wet	wet ducks the reverb. all ducks the mixed output including dry. the sidechain button cycles off, wet and all.
reverse	off / on	off	plays overlapping sections of the wet tail backwards. length sets the reversal window, limited to 0.4 to 2 seconds.
freeze	off / on	off	holds the existing late tail and stops new input entering the loop. tap toggles the latch. hold longer than 300 ms from off for momentary freeze. double-clicking length toggles the latch without moving length.
bypass	off / on	off	bypasses reverb processing. i use it to compare the input with the processed result.
range low	20 to 2,000 hz	20 hz	removes low frequencies from the signal feeding the late tail. at 20 hz this filter is bypassed.
range high	500 to 20,000 hz	20,000 hz	removes high frequencies from the signal feeding the late tail. at 20,000 hz this filter is bypassed.
tail eq frequency	20 to 20,000 hz	80 / 500 / 3,000 / 10,000 hz	positions each of the four wet-output eq bands. these controls shape the reverb after the late loop.
tail eq gain	-12 to +12 db	0 db	boosts or cuts the selected wet frequency region. the dry signal is unchanged.
tail eq width	0.3 to 6	1	changes each band's width. higher values make bell bands narrower.
tail eq enable	off / on	off	enables the individual band. disabled bands do not apply their eq settings.
tail eq routing	stereo / mid / side / left / right	stereo	selects the component processed by that band. each band has its own routing choice.
tail eq shape	bell / shelf	bell	switches the lowest or highest node between bell and shelf. the two middle nodes remain bells.

characters

room, hall and cloud change the delay, diffusion and decay settings. i compare them on the same source before adjusting length.

room

room combines early reflections with a late tail. the early reflections keep the source's direction, while the late loop receives the mid signal.

hall

hall uses its own early-reflection pattern and late-tail settings. it also keeps the early reflections separate from the mid-fed late loop.

cloud

cloud omits the early-reflection contribution and spreads input to the late loop over one second. auto comp stays at unity, so it does not adjust the wet gain.

spectral display

frequency runs horizontally. the spectrum shows signal level by frequency. normally it shows the dry input; with delta on, it shows the wet signal with the dry spectrum behind it.

the decay curve shows decay-time targets relative to length. i read that separately from the spectrum level and the editable tail eq curve.

i drag the tail eq nodes to change frequency and gain, and use the mouse wheel over a node to change its width. the edge handles set the frequency range feeding the late tail.

latency

open reports 256 samples of latency, about 5.8 ms at 44.1 khz. there is no live button.

i check the host's plugin delay compensation setting when placing open in a session. reverse's delayed swells are part of the effect; turning it on does not change the reported latency.

presets

i use presets as starting points, then adjust depth for the source. click the preset name to open the menu, or use the arrows to browse.

the menu groups presets by room, hall and cloud. choose init to return to the parameter defaults listed above.

how it works

input analysis

open measures the main input across frequency bands. focus and bloom use those measurements to change the decay targets.

early reflections

room and hall send early reflections to the wet output alongside the late tail. cloud skips that contribution.

late tail

a feedback delay network circulates audio through delays and filters. the decay targets control how that energy fades by frequency. cloud spreads the incoming excitation before it reaches the loop.

output

reverse plays sections of the wet tail backwards. tail eq and tone shape the wet signal. depth blends it with the dry input, and sidechain can duck the reverb or the mixed output.

specifications

specification	detail
cpu	about 3% on macOS at 44.1 kHz, single instance (ROOM about 2.4%, HALL and CLOUD about 3%)
formats	VST3 / AU
platforms	macos + windows
mac requirements	macos 10.13+ (intel) or 11+ (apple silicon)
windows requirements	windows 10+, 64-bit
license	lifetime license. no ilok, no account, no subscription. offline use.

installation

get open from the product page.

macos

copy KERN OPEN.vst3 to ~/Library/Audio/Plug-Ins/VST3/.
for au, copy KERN OPEN.component to ~/Library/Audio/Plug-Ins/Components/.
rescan plugins in the host. look for KERN OPEN under KERN Audio.

windows

copy KERN OPEN.vst3 to C:\Program Files\Common Files\VST3\.
rescan plugins in the host. look for KERN OPEN under KERN Audio.

quick start

an insert

i place open on the source and choose init from the preset menu.
i compare room, hall and cloud, then set length for the phrase.
i adjust depth to blend the tail, then compare with bypass.

a shared return

i place open on a return and set depth to 100%.
i send sources to that return and balance them with their send levels.
if i want the source to duck the tail, i select sidechain wet. i can route an external key to duck it from another track.

a frozen tail

i play a source until there is a tail to hold.
i tap freeze to latch it, or hold the button for momentary freeze.
i release a held button, or tap again to unlatch. if length is in its freeze region, i lower it as well.

tips

where in the chain

i start with an insert when one source needs its own space, adjusting depth to blend it. on a shared return, i set depth to 100% and use send levels to balance the sources.

i use a post-fader send when reverb should follow the source fader, or pre-fader when i want independent feeding of the return. i put corrective processing before open to change what excites the tail; processing after open shapes its output.

i leave headroom and check the return after boosting tone or eq. auto comp is not a peak limiter, and cloud does not apply automatic gain compensation.

i also listen to the return in mono before settling on its level.

troubleshooting

what i hear	what i check
silence in delta	i raise depth. delta follows the wet level, so depth at 0% is silent. i also check that there is input or an existing tail.
the tail keeps holding	i turn freeze off and bring length below 11.95 s. either control can hold the tail.
sidechain seems inactive	i cycle the sidechain button to wet or all. for an external key, i check the host routing. without an external connection, it uses the dry input.
the dry signal ducks too	i switch the sidechain target from all to wet.
auto has no effect in cloud	cloud holds compensation at unity even when auto is on. i set the output balance with depth and the track or return level.
focus seems inactive	i check bloom. at 50%, focus does not change the decay-time mapping.
open does not appear in the host	i check the installation paths above, then rescan plugins.

keyboard / mouse reference

action	control
adjust a knob	click and drag
fine-adjust depth, length, focus or tone	shift + drag
latch or release freeze	tap freeze, or double-click length
momentary freeze from off	hold freeze longer than 300 ms, then release
change tail eq frequency and gain	drag a node horizontally and vertically
change tail eq width	mouse wheel over a node
fine-adjust tail eq	shift + drag a node
enable or disable a tail eq band	double-click its node
type tail eq values	double-click its label
choose tail eq routing	right-click its node
change an outer band's shape	click its type badge
change the range feeding the tail	drag a spectrum edge handle
reset a range cutoff	double-click its edge handle
browse presets	click the header arrows
open the preset menu	click the preset name

version history

v1.0.0 (september 2026)

initial release. room, hall and cloud, with tail eq, freeze, reverse and sidechain ducking. the late loop receives the mid signal. cloud spreads incoming excitation and holds auto comp at unity.

open / user manual